1. Field of the Invention
The present invention relates to a vehicle navigation system and method for guiding a vehicle to a destination in accordance with a navigation route. More specifically, the present invention relates to a vehicle navigation system adapted to provide the user with information for navigation to a destination even when the vehicle enters a narrow street (hereinafter referred to as a xe2x80x9cminor streetxe2x80x9d for convenience), such as a small neighborhood road, which has not been searched by route guidance.
2. Description of the Related Art
In the description below, the term xe2x80x9cvehiclexe2x80x9d generally refers to an automobile, but is not limited thereto.
A typical vehicle navigation system includes a map-data storage device, such as a CD-ROM, DVD-ROM, or IC memory card, in which map data has been stored in advance; a display device; a GPS (global positioning system) receiver; and sensors, such as a gyroscope and a vehicle speed sensor, for detecting the current location and orientation of the vehicle. The map data for an area including the current location of the vehicle is read from the map-data storage device, and a map image for the vicinity of the vehicle is rendered on the display screen based on the read map data. A mark representing a vehicle location is also displayed on the map image on the display screen. The map image can be scrolled on the screen in response to the movement of the vehicle or the vehicle location mark can be moved with the map image being fixed on the screen, thereby allowing a user to recognize at a glance where the vehicle is currently travelling.
The vehicle navigation system commonly incorporates a function (a route navigation function) for guiding the user to travel with ease toward a destination without taking a wrong road. Using map data, the route navigation function automatically searches for an optimum route (typically, the most cost-effective route) connecting from a starting point (e.g., the current location of a vehicle) to a destination by performing a simulation, employing a breadth-first search method, the Dijkstra method, or the like, and stores the route found by the search as a navigation route. When travelling, the navigation route is displayed on a map image in a distinct manner (e.g., in a different color or in a broader line) from the other roads, and when approaching a predetermined distance from an intersection at which the vehicle is to make a turn on the navigation route, a guide map (an enlarged intersection map and an arrow indicating a new travel direction at the intersection) or the like is displayed, thereby allowing the user to grasp an optimum route to a destination.
Prior to route searching, the user sets a destination and, as required, a way point on the way thereto (i.e., which route should be taken to reach the destination). If necessary, the user additionally sets various conditions (e.g., whether or not a toll road should be taken and/or whether priority should be given to distance or driving time). Based on the set data, the navigation system searches for a plurality of routes to the destination, displays the found routes in different colors, and guides the user in accordance with a route selected by the user from among the routes found.
In such route guidance, a conventional navigation system separately stores road data for route guidance and road data for display, and thus uses the former road data for route searching and route guidance and uses the latter road data for displaying the map. In this case, the road data for route guidance is stored together with associated traffic regulation information (e.g., no left/right turn, wrong way) for each road and cost data, such as distance and time, used for searching for a recommended route. However, data for, for example, minor streets, such as small neighborhood roads, is not included in the road data for route guidance because part of the traffic regulation information thereof has not been surveyed. As a result, while minor streets are displayed on the map based on the road data for display, in practice, they are not searched by route searching (and are not used for route guidance).
In such a conventional vehicle navigation system, as described above, since minor streets are only displayed on the map and are not searched by route searching (and are not used for route guidance), the conventional vehicle navigation system has a problem in that, in particular, in an area where there are many minor streets, such as in an urban area, the set starting point or the destination may be far from a recommended road. The conventional navigation system also has a problem in that it cannot provide the user with detailed information for guiding him or her from a starting point to a navigation route or from the navigation route to the destination.
In addition, when the vehicle goes off an intended guidance route and the driver loses his or her way on a minor street, the conventional navigation system has a disadvantage in that the user feels a sense of insecurity, thereby making it difficult for him or her to drive safely.
In the future, it is predicted that traffic regulation information will be expanded to cover minor street data. If, however, minor street data that is associated with and minor street data that is not associated with traffic regulation information coexist, it is difficult to distinguish therebetween. In such a case, the minor street data that is not associated with traffic regulation information is excluded from data that is used for route searching (route guidance), as in the conventional manner. The result is that such an arrangement still cannot provide detailed guidance information to a destination.
The present invention has been made in view of the foregoing deficiencies of the related art, and an object of the present invention is to provide a vehicle navigation system which can offer information for reliable navigation to a destination even when a vehicle has entered a minor street, and which can enhance usability so that the user can travel with an increased sense of security.
To overcome the foregoing problems of the related art, the vehicle navigation system according to the present invention includes a vehicle-location determination unit for determining the current location of a vehicle; an information input unit (operation unit) for inputting a destination and information necessary for searching for a route; and a display unit for providing the user with guidance information. The vehicle navigation system further includes a first data storage unit for storing map data including road data for display and road data for route searching and a second data storage unit (database) for storing road data concerning narrow streets, having a predetermined width or below, which are not included in the road data for route searching; and a controller connected in a controllable manner with the vehicle-location determination unit, information input unit, display unit, and the first and second storage units. During route guidance to a destination on the screen of the display unit, based on the road data for route searching, the controller determines whether or not the vehicle has entered a minor street by referring to the map data. When the controller determines that the vehicle has entered a minor street, the controller sets the point of entry into the minor street as a new starting point and searches again for a route to the destination using the minor streets and causes the screen of the display unit to be divided into first and second screens. Based on the result of the repeated search and the road data for minor streets, the guidance route is displayed unmodified on the first screen, and the minor street is displayed on the second screen in an enlarged form relative to the first screen.
According to the vehicle navigation system of the present invention, therefore, when a vehicle enters a minor street during route guidance to a destination on the screen of the display unit, the display screen is divided into first and second screens. Based on the result of the repeated search and the road data for minor streets, the guidance route is displayed unmodified on the first screen, and the minor street is displayed on the second screen in an enlarged form relative to the first screen. Accordingly, the present invention provides a vehicle navigation system that provides information for reliable navigation to a destination even when a vehicle enters a minor street.
With this arrangement, the user can obtain a detailed guidance route (in this case, a minor street) with the second screen, which is displayed in an enlarged form, on the display unit, and can drive the vehicle, unlike in the related art, with a sense of security while following the guidance route.